This invention relates to a novel construction for ring laser angular rates sensors and more particularly to a construction of a mirror assembly for such sensors which is less costly to manufacture than prior art constructions.
After years of development, ring laser angular rate sensors, commonly referred to as ring laser gyros, have become commercially successful products. Today, most commercial ring laser angular rate sensors use a mechanically and thermally stable block construction and mechanical dither concepts taught in U.S. Pat. No. 3,390,606, issued to T. Podgorski, and U.S. Pat. Nos. 3,467,472 and 3,373,650, both of which were issued to J. Killpatrick.
These prior art ring laser angular rate sensors have proven highly satisfactory in operation. These prior art ring laser angular rate sensors, however, are costly to manufacture.
A key element of a ring laser angular sensor is the mirror assembly. The mirror assemblies, using prior art construction techniques, include a substrate which is usually of a material which is the same as that chosen for the laser block which contains a cavity filled with gas. The block and mirror substrates may be, for example, Cervit, Zerodur, Fused Silica, BK-7 glass, etc.
The mirror assembly substrates of the prior art have at least one highly polished surface. Multi-layer dielectric coatings are deposited directly on the highly polished substrate surface to form a mirror. Secondly, the highly polished substrate can be joined with a matching highly polished block in order to fix the mirror substrate assembly to the block by, what is referred to as, an optical contact technique. That is, the surfaces are so higly polished that when the substrate and block are pressed together, the substrate is fixed to the block without bonding agents.
As is well known to those skilled in the art, the mirrors are the critical components of a ring laser angular rate sensor. This is so since a poor mirror does not achieve superior reflectivity required by a laser angular rate sensor. Reflectivity of the mirror is normally desired to be 99.9%. Poor reflectivity results in scattering of the laser beams in the ring laser which in turn causes a degradation in rate sensor performance. In order to achieve superior reflectivity, the substrates require extreme measures to achieve an ultra-high polished surface before the coatings are deposited thereon. To achieve an ultra-high polished mirror substrate surface usually requires several days of abrasive polishing.
After the step of ultra-high polishing of the mirror substrate's surface, the multi-layer coatings are deposited. The final step in the mirror assembly process is a quality check. If the mirror assemblies fail the quality check, the polishing step and deposition step must be repeated. For these reasons, the mirror assemblies are very costly to produce.